Internal combustion engines (ICE's) are often called upon to generate considerable levels of power for prolonged periods of time. Many such engines employ a boosting device, such as an exhaust gas turbine driven turbocharger or a mechanically-driven supercharger, to compress the airflow before it enters the intake manifold of the ICE in order to boost the engine's power and efficiency.
Considered broadly, both turbochargers and superchargers function as gas compressors that force more air and, thus, more oxygen into the combustion chambers of the ICE than is otherwise achievable with ambient atmospheric pressure. The additional mass of oxygen-containing air that is forced into the ICE improves the engine's volumetric efficiency, allowing it to burn more fuel in a given cycle, thereby increasing combustion pressures and generating more power.
In an effort to increase overall engine efficiency and response, some ICE's employ multi-stage boosting systems. Such boosting systems may include turbocharging systems with a smaller turbocharger that is more effective at lower exhaust flows and a larger turbocharger that is more effective at higher exhaust flows or a combined system having a mechanically- or electrically-driven supercharger and an exhaust-driven turbocharger. A transition between two turbochargers or supercharger and turbocharger in such boosting systems is typically controlled based on the particular engine's configuration and operating requirements.